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5. A Potash Apparatus.—Several forms of potash apparatus
are made ; that of Geissler (Fig. 6), and Classen (Fig. 7) being
perhaps most commonly employed. The latter has the advan-
tage of being very light. The removable side tube is filled
with granulated calcium chloride or soda-lime, with a plug of
cotton wool at each end. The bulbs of the apparatus are filled

FIG. 5

with a strong solution of caustic potash containing 25 grams of
potash to 50 c.c. of water. This is done as follows. Remove
the soda-lime tube and attach in its place a piece of rubber             !

tubing.     This   serves   as a mouthpiece.     Pour   the   potash             ;

solution into a basin and dip the other end of the potash
apparatus under the liquid. Suck at the rubber tube until the             V

quantity appears   sufficient to  fill   the bulbs.     Remove   the             ¥

potash solution and continue to suck until the solution is trans-
ferred to the bulbs. The bulbs should be nearly filled. In the
case of Classen's apparatus, the liquid should stand half an inch
deep in the bottom of the apparatus outside the lowest bulb.

Wipe the potash solution from the outside and inside of the
inlet tube of the apparatus with filter paper. Smear a thin film
of vaseline on the ground end of the soda-lime tube before
replacing it, and fit to the open ends of the apparatus, stoppers
of rubber and glass rod, which are not removed, except when
the apparatus is in use. As the potash apparatus has jo be